1. Field of the Invention
The present invention relates to a semiconductor device having a plurality of interconnection layers and to a production method for the semiconductor device.
2. Description of Related Art
Semiconductor devices generally include a semiconductor substrate, a functional device provided in a surface of the semiconductor substrate, and a multi-level interconnection structure provided on the semiconductor substrate. The multi-level interconnection structure typically includes a plurality of interconnection layers stacked with the intervention of interlevel insulation films, and connection between the interconnection layers is achieved through contact holes formed in the interlevel insulating films.
Aluminum is conventionally employed as an interconnection material, but has a limitation in reduction of the resistance of the interconnection. As the sectional area of the interconnection is reduced with microminiaturization of the semiconductor device, a problem associated with the resistance of the interconnection arises. Particularly, there is a demand for reduction of the resistances of a ground line and a power line.
In this connection, the inventor of the present invention, for example, has proposed in Japanese Unexamined Patent Publication (KOKAI) No. 2002-217284 that a gold layer is employed as an uppermost interconnection layer for the reduction of the resistance of the interconnection.
In this prior art, a barrier layer of a titanium thin film is disposed between an aluminum interconnection layer and the uppermost gold interconnection layer electrically connected to each other through a contact hole, so that migration of aluminum is prevented by the barrier layer.
However, gold is a highly diffusible material. Where the semiconductor device is allowed to stand at a high temperature for a long period of time (e.g., at 400° C. for 30 minutes to 1 hour) in an alloying process, for example, gold easily diffuses into the aluminum interconnection layer.
In addition, the titanium thin film has a poor anti-corrosion property. Where the semiconductor device is used in an environment like a pressure cooker test (PCT) environment, the aluminum interconnection layer is liable to be corroded, resulting in breakdown of the semiconductor device.